USB: unusual_devs entry for A-VOX WSX-300ER MP3 player

This patch (as763) adds an unusual_devs entry for the A-VOX WSX-300ER MP3
player.

From: David Kuehling <dvdkhlng@gmx.de>
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>